Zhu Lin

Date of Award


Degree Type


Degree Name

Master of Science




Dr. Leonard G. Luvt


Orexin A (33 amino acids) and orexin B (28 amino acids) are two naturally occurring ligands of the G-protein coupled receptor: orexin receptor 1 (OXiR) and orexin receptor 2 (OX2R). Based on the expression of OXiR in colon cancer cells, gallium-68 labelled orexin A (15-33) and orexin B (6-28) were developed as potential PET imaging agents targeting colon cancer cells. Orexin A (15-33) and orexin B (6-28) were synthesized by Fmoc solid phase peptide synthesis (SPPS). A bifunctional chelator 1,4,7,10-tetra azacyclo dodecane- N,N',N”,N”'-tetraacetic acid (DOTA) was used to attach gallium-68 to orexin A (15-33) and orexin B (6-28). A linker aminohexanoic acid (Ahx) was incorporated between the targeting peptide sequence and 68Ga-DOTA complex to reduce the bulky effect of the imaging label on the binding affinities. It was determined that the IC50 values of Ga-DOTA-Ahx-orexin A (15-33) and Ga-DOTA-Ahx-orexin B (6-28) were 629 nM and 168 nM respectively. In order to evaluate the binding affinities in cells, orexin A (13-33) and orexin B (6-28) were also labeled with fluorescein isothiocyanate (FITC) allowing for fluorescence microscopy studies. Besides orexin A and orexin B analogues, a potential orexin receptor antagonist was developed as a potential imaging agent as well and preliminary synthetic steps were undertaken. This antagonist was proposed to be labelled with fluorine-18 to form the compound [l8F](4-fluoro-phenyl)-(4-quinozolin- 2-yl-[l,4]diazepan-l-yl)-methanone as an imaging agent targeting colon cancer cells



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